retroforth/doc/book/tech-notes/kernel-words
crc 6a4aaf8eac prefix: namespace is now sigil:, rename words, update examples, update docs
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## On The Kernel Wordset
In implementing the RETRO 12 kernel (called RETRO Core, and
defined in `image/retro.muri`) I had to decide on what functionality
would be needed. It was important to me that this be kept clean
and minimalistic, as I didn't want to spend a lot of time
changing it as time progressed. It's far nicer to code at the
higher level, where the RETRO language is fully functional, as
opposed to writing more assembly code.
So what made it in?
Primitives
These are words that map directly to Nga instructions.
dup drop swap call eq? -eq? lt? gt?
fetch store + - * /mod and or
xor shift push pop 0;
Memory
fetch-next store-next , s,
Strings
s:to-number s:eq? s:length
Flow Control
choose if -if repeat again
Compiler & Interpreter
Compiler Heap ; [ ] Dictionary
d:link d:class d:xt d:name d:add-header
class:word class:primitive class:data class:macro
sigil:: sigil:# sigil:& sigil:$
interpret d:lookup err:notfound
Assembler
i d r
I *could* slightly reduce this. The $ sigil could be defined in
higher level code, and I don't strictly *need* to expose the
`fetch-next` and `store-next` here. But since the are already
implemented as dependencies of the words in the kernel, it would
be a bit wasteful to redefine them later in higher level code.
A recent change was the addition of the assembler into the
kernel. This allows the higher levels to use assembly as needed,
which gives more flexibility and allows for more optimal code
in the standard library.
With these words the rest of the language can be built up. Note
that the RETRO kernel does not provide any I/O words. It's assumed
that the RETRO interfaces will add these as best suited for the
systems they run on.
There is another small bit. All images start with a few key
pointers in fixed offsets of memory. These are:
| Offset | Contains |
| ------ | --------------------------- |
| 0 | lit call nop nop |
| 1 | Pointer to main entry point |
| 2 | Dictionary |
| 3 | Heap |
| 4 | RETRO version identifier |
An interface can use the dictionary pointer and knowledge of the
dictionary format for a specific RETRO version to identify the
location of essential words like `interpret` and `err:notfound`
when implementing the user facing interface.